Formable composites are known for use in electrical applications. These composites are generally utilized as supporting substrates, insulating layers, and/or casements for electrical devices. Ideally, the composite materials provide excellence with regard to both electrical and mechanical properties, e.g., high circuit density, low transmission energy loss, high strength, low weight, etc., and provide all desired characteristics at low cost. Problems still exist with attaining this ideal, however.
Formable composite materials generally include reinforcement fibers held in a polymer matrix, often with additional components as well to improve characteristics such as thermal conductivity, adhesion, color, etc. Unfortunately, components that make up a composite, while supporting one or more desired properties, often detract from others. For instance, glass fibers can offer excellent tensile strength characteristics, but have a dielectric constant of about 6, and thus are often unsuitable for low transmission energy loss applications, particularly if used in abundance. Other fibers that have been used in forming reinforced composite materials have included aramid fibers such as Kevlar™ fibers and ultrahigh molecular weight polyethylene (UHMWPE) fibers. These reinforcement materials likewise present drawbacks to a composite such as high material or processing costs, low thermal resistance, high dielectric loss, and the like.
In an attempt to mitigate problems associated with high strength fibrous reinforcement materials, fibers have been combined with resins that exhibit, for instance, desirable electrical characteristics, low costs, etc., to form composites having more acceptable electrical as well as physical properties. For instance, epoxy resins have often been utilized due to their good processability and low costs, though with a dielectric constant in the range of 3.0 to 3.5, the composite materials formed with an epoxy resin can still exhibit less than ideal electrical characteristics.
Fluoropolymers have also been examined as possible matrix material for a composite electrical substrate. For instance, fiber-reinforced composites formed with a poly(tetrafluoroethylene)-based matrix have obtained improved electrical properties over epoxy composites, e.g., dielectric constants less than 2.5 and loss tangents (i.e., dielectric loss) less than 0.002, but have done so at the sacrifice of mechanical characteristics. Moreover, fluoropolymers are often expensive and difficult to process, increasing the costs associated with such composites.
While there have been improvements in materials and methods for forming composites for use in electrical applications, there remains room for further improvement and variation within the art.